Modelling topographic potential for erosion and deposition using GIS

Abstract

Modelling of erosion and deposition in complex terrain within a geographical information system (GIS) requires a high resolution digital elevation model (DEM), reliable estimation of topographic parameters, and formulation of erosion models adequate for digital representation of spatially distributed parameters. Regularized spline with tension was integrated within a GIS for computation of DEMs and topographic parameters from digitized contours or other point elevation data. For construction of flow lines and computation of upslope contributing areas an algorithm based on vector-grid approach was developed. The spatial distribution of areas with topographic potential for erosion or deposition was then modelled using the approach based on the unit stream power and directional derivatives of surface representing the sediment transport capacity. The methods presented are illustrated on study areas in central Illinois and the Yakima Ridge, Washington.     

A support for the existence of paleolakes and paleorivers buried under Saharan sand by means of “gravitational signal” from EIGEN 6C4

The goal of this study is to demonstrate that and how the recent gravitational and topographic data support the findings made by geologists and others as for the existence of the paleolakes and paleoriver systems, now buried under the sands of Sahara. It is always important and useful to have such an independent analysis supporting certain results, and this paper is such a case. We make use of the gravity disturbances (or anomalies), the Marussi tensor of the second derivatives of the disturbing geopotential, the gravitational invariants and their certain ratio, the strike angle and the virtual deformations. The geopotential is represented by the global combined (from satellite and terrestrial data) high-resolution gravity field model EIGEN 6C4 (till degree and order 2160 in spherical harmonic expansion). The topography is derived from the ASTER GDEM and ETOPO 1 models (both are used). With all these data, we confirm the existence of huge paleolakes or paleoriver systems under the Saharan sands known or anticipated in an independent way by geologists for the lakes MegaChad, Fazzan and Chotts; for Tamanrasset river valley; and Kufrah Basin, presumptive previous flow of the Nile River. Moreover, we suggest a part of the Grand Egyptian Sand Sea as another “candidate” for a paleolake and hence for a follow-up survey.     

Long-term variations in geomagnetic and solar activities and secular variations of the geomagnetic field components

Summary After the removal of the eleven-year periodicity, long-term patterns of the aa indices of geomagnetic activity and of Wolf's sunspot numbers are defined. The positions of maxima and minima exhibit the same regularities as the secular variations of the geomagnetic filed components. This result is associated with the motion of the Sun round the barycentre of the solar system.Presented at symposium Planet 88, Tihany, September 1988.     

Investigation of the damping of geomagneticPi2 pulsations using generalized spectral analysis

Summary The method of spectral analysis has been modified to render the spectrum not only a function of frequency, but also of damping. The generalized spectra of damped geomagnetic pulsations, recorded at the observatories of Budkov and Dymer, are computed. The degree of damping of these pulsations in the X and Y-components at both stations is determined. The results are compared with results obtained using other methods.     

On the question of coronal holes as sources of geomagnetic disturbances

Summary Using a more detailed geomagnetic activity Kp index, the finding in [3] that geomagnetic activity increases after the CMP of coronal holes, was verified; it was shown using individual activity patterns, that coronal holes apparently do not form a homogeneous class of phenomena, which must be respect in considerations of emissions of fast solar wind streams.     

Combinations of Satellite Crossovers to Study Orbit and Residual Errors in Altimetry

We define combinations of dual‐ and single‐satellite crossover differences to isolate both stationary orbit‐geopotential and non‐geopotential errors in altimetry data. Specifically two types of combinations are found useful. While no combination of differences can resolve the full radial error of single or paired satellites, an approximation of the mean or geographically correlated error of the generally dominant lower orbit of a pair can be found from one kind (substitutions). (The variable part of the error is always available from the single‐satellite crossover differences.) A second useful combination type is found to yield no geopotential orbit error (zeros): uniquely, these can reveal errors in altimetry from imperfect media corrections as well as oceanographic changes in sealevel. The later circumstance is particularly important when the missions for a pair of satellites are disparate in time. This revised version was published online in July 2006 with corrections to the Cover Date.